Answer:
a. tried - I tried to solve the puzzle but couldn't figure it out.

b. baked - I baked a cake for my sister's birthday party.

c. drank - I drank a glass of water after exercising.

Explanation:

Simple past tense is used to describe an action or event that occurred in the past and is now completed. To form the simple past tense, we usually add "-ed" to the base form of the verb for regular verbs. For irregular verbs, the past tense form is not formed by adding "-ed", instead, it has a unique past tense form.

In the given sentences, "try" becomes "tried" in simple past tense, "bake" becomes "baked" and "drink" becomes "drank".